This invention is concerned with locating and constraining magnetisable members on components of electrical machines. More particularly it is concerned with locating and constraining such members on the rotors of such machines.
The use of rare-earth permanent magnets to provide the excitation field in alternating current (AC) machines is known. However, the handling and mounting of members of rare-earth material is not straightforward. Such members are brittle and are therefore easily damaged. Consequently, it is difficult to mount the members onto a rotor or a stator of an AC machine in such a way that they can withstand the large forces exerted on them during operation, without sustaining damage.
U.S. Pat. No. 6,037,696 discloses a rotor for use in an electrical machine wherein magnetised members are mounted on a surface of a disc-shaped central sheet. The rotor disc of U.S. Pat. No. 6,037,696 includes a braced hub in the form of a spider that is for restraining the central sheet and promoting rotor rigidity. The magnetised members are constrained axially and tangentially on the central sheet by being bonded face-to-face with the surface thereof. The magnetised members are constrained radially on the central sheet by the provision of a circumferential lip that is formed integrally with the central sheet. Further radial constraint is provided by bonding a radially innermost edge of each magnetised member to the braced hub.